The goal of these proposed studies is to examine the histologic and physiologic properties of jaw muscles in a convenient animal model, the rabbit digastric muscle. The relationship between whole muscle length, muscle sarcomere length, whole muscle force and jaw position will be measured with microscopic methods, isotonic records and cineradiographs. These studies are expected to further our presently poor understanding of the way in which jaw muscles shorten and develop force in a particular mammalian system.